I found this a good site re auditory processing www.apduk.org/
As far as I understand APD is a bit like dyslexia of the brain. There may be nothing wrong with the child's hearing - they can hear the normal range of sounds - but it is a problem with how the brain interprets that noise into meaningfull understandable sound/speech.
It is not a problem that will go away but you can find strategies that may help him socially and educationally. You may even find that you have been unconsciously incorporating some strategies into his life already.
This is the advice we received from SALT
regarding school, you may find it useful
Auditory Processing problems
May need reminding what has been asked, could help to have written instructions, but even with written instructions it needs to be checked that he fully understands what is required.
May help to have name repeat instructions, if it appears he doesn?t understand, hasn?t got the instructions in order. If the information needs to be repeated, give the same instruction in the same way/order, don?t change it as this can increase the chance of him getting it wrong ? brain can view it as two separate processes to contend with.
It could benefit name to sit at the front of the class, with the ability to see teachers face, preferably with any direct light on the teachers face rather than coming from behind (creates shadow affects visual stimulus).
If asking a question of name he may need extra time to process what is being requested and extra time to respond.